Pneumatic abrasive cutting tool



Sept. 11, 1962 Filed Nov. 17, 1960 R. w. JOHNSTON ET AL 3,053,016

PNEUMATIC ABRASIVE CUTTING TOOL 2 Sheets-Sheet 1 INVENTORS ROBERT w. JOHNSTON ROBERT D. HALL AT-TORNEY Sept. 11, 1962 R. w. JOHNSTON ETAL 3,053,016

PNEUMATIC ABRASIVE CUTTING TOOL 2 Sheets-Sheet; 2

Filed Nov. 17, 1960 JNVENTORS ROBERT w. JOHNSTON ROBERT D. HALL ATTORNEY United States Patent 3,053,016 PNEUMATIC ABRASIVE CUTTING TOOL Robert W. Johnston, San Jose, and Robert D. Hall, Los Altos, Calif., assignors to Sylvania Electric Products, Inc., a corporation of Delaware Filed Nov. 17, 1960, Ser. No. 69,846 9 Claims. (Cl. 51-8) This invention relates to abrasive cutting apparatus, and more particularly to a pneumatic abrasive cutter in which a mixture of abrasive particles and air (or other gas) under pressure is expel-led at high speed from a nozzle.

The very nature of fine abrasive powders used in cut ters of this type causes problems of wear in moving parts of the cutting apparatus itself. For example, valves, venturi tubes, etc. associated with the abrasive feeding mechanism, being in or adjacent to the path of flow of the particles, are especially susceptible to wear. Some prior art devices use a combined gravity and shaker feed technique to inject the abrasive into the jet stream, but electrical meters and contacts, the many moving parts, noise, and attendant vibration involved in such apparatus are unavoidable and undesirable.

A general object of our invention is the provision of abrasive cutting apparatus with relatively few moving parts, none of which are exposed to the abrasive particles used in the system.

Another practice followed by the prior art is continuous feeding of abrasive particles by aspiration into the jet air stream. The disadvantage here is that there is a minimum diameter of nozzle opening which must be maintained in order that there shall be suflicient velocity in the feed line to draw abrasive particles into the jet stream. Since the size of nozzle opening dictates the minimum width of cut possible with the tool, this system of feeding imposes a limitation on the performance of the tool in this respect.

Another object of our invention is the provision of a system for feeding abrasive particles into the jet stream of an abrasive cutter in such a manner that the diameter of the cutter nozzle opening may be reduced substantially below that required for continuous feeding of abrasive particles into the jet stream.

Other objects of our invention are the provision of an abrasive cutter with a minimum number of moving parts; the provision of a cutter of this type in which the feeding mechanism is powered solely by pneumatic pressure of the system itself; and the provision of a low-cost, lightweight, compact pneumatic cutter which requires very little maintenance.

These and other objects of our invention will become apparent from the following description of a preferred embodiment thereof, a reference being had to the accompanying drawings in which FIG. 1 is an assembly drawing of abrasive cutting apparatus embodying our invention, the principal parts of the apparatus being shown in section;

FIG. 2 is a greatly enlarged sectional view of the valve part of the va-lving mechanism of our invention;

'FIG. 3 is a plane view of the top of the valve stem as viewed on line 3-3 of FIG. 2; and

'FIGS. 4-6, inclusive, are schematic diagrams showing the operation of the abrasive feeding mechanism.

Briefly, our invention is based on a pressure differential feeding system wherein a pressure differential is applied momentarily and cyclically across the tank containing the abrasive particles to positively inject the particles into the jet stream. This pulse-type feeding system results in periodic injection of a predetermined quantity or charge of particles into the air stream. The length of the hose 3,053,016 Patented Sept. 11, 1962 between the injection point and the nozzle, together with the back pressure effect of the small nozzle opening, effectively averages out these pulses so that the air abrasive particle mixture flows from the nozzle in a practically uniform continuous stream. The pulse of differential pressure in the line is derived from a pneumatically operated pressure release va-lving mechanism located between the abrasive injection point and the source of line pressure. During operation pressure is maintained above and below the abrasive. Momentary reductions of pressure on the underside of the abrasive caused by the valving mechanism produces the pressure differential pulses which push charges of abrasive particles into the jet stream.

Referring now to the drawings, FIG. 1 shows a system comprising a source of pneumatic pressure 10 connected by on-oif valve 11 to a conduit '12, which may be pipe or metallic tubing. A flexible conduit or hose 14 secured to conduit :12 makes connection at the opposite end to a nozzle :15 which has a wear-resistant head 16 formed with an opening 17 through which abrasive-charged air is ejected in the direction of the arrow at high velocity to provide the cutting action.

A tank 19 containing abrasive material 20, such as aluminum oxide powder, is mounted above conduit 12 and is connected thereto by a feeder conduit 22 which opens directly into conduit 12 at point A and which has an extension 23 projecting into the bottom of the tank. In order to prevent uncontrolled flow of abrasive material into the feeder conduit 22, the upper end of extension 23 is closed and the extension side wall has a feed opening 24 therein. Abrasive particles pass from the tank through hole 24 into conduit 22 and join the jet stream, indicated by the arrows, in conduit 12 at point A.

A removable cap 25 in the top of tank 19 provides access to tank for replenishing the supply of abrasive powder 20. In accordance with our invention, the space in tank 19 above the abrasive material is pressurized while the apparatus is operating. In order to relieve this pressure when the apparatus is turned oif, the top of the tank is connected by line 26 to a pressure relief valve 27 having an exhaust outlet 28. Valve 27 is normally closed by the pressure in line 26 acting against valve head 29 which presses against seat 30. Valve 27 is opened when valve stem 31, and thus head 29, is dis.- placed to the left, as viewed, by cam arm 35 on control handle 36 of main valve 11. This occurs when handle 36 is rotated to close valve 11, and the pressure in the upper part of the tank is thus relieved when pressure in the main line is turned off. When on-ofi valve 11 is opened, air under pressure from source 10 enters the tank via conduit 12, feeder conduit 22 and feed hole 24; and arm 35 allows relief valve 27 to close and thus permit full pressurization of the tank.

In order to positively feed abrasive material into the jet stream, a pneumatically-operated valving mechanism 38 is connected to conduit 12. Mechanism 38 comprises a cylinder 40, a plunger 41 movable in the cylinder, and a valve 42 in the base of the cylinder and actuated by plunger 41. Air from conduit 12 passes to cylinder 40 through conduit 43 connected to conduit 12 at a point C between pressure source 10 and injection point A. Conduit 43 is fastened to cylinder 40 by fitting 44, the upper end of which is fitted with an elongated valve 42.

Valve 42 comprises an elongated tubular rubber-like insert 45, see FIG. 2, the lower end 45a of which forms a valve seat, and a vertically movable member 46 con.- sisting of a stem 47 extending through the insert and carrying a head 48 adapted to press against seat 45a to close the valve. The upper end of stem 47 has a scallopshaped flange 49, see FIG. 3, which limits the downward travel of the movable member. The bore 50 of insert 45 has a diameter larger than that of stem 47 and valve head 48 has a cross-sectional dimension smaller than the inner diameter of adjacent parts of fitting 44. Accordingly, when the valve head is displaced from the seat 45a, downward as viewed, air escapes from main pressure line 12 through conduit 43 and insert 45 into cylinder 40. The scalloped shape of flange 49 insures that the top of insert bore 50 will be opened to cylinder 40 when the flange engages the top of insert 45. This condition occurs only when valve 11 is in the off position and the conduits have become depressurized.

The movable member 46 of the valve 42 closes in response to pressure in line 12, and opens either when line pressure is turned olf or when member 47 is forcibly depressed.

Plunger 41 has a diameter slightly less than the inside diameter of cylinder 40 in which it fits and has a guide stem 54 projecting upwardly from the plunger through a :guide opening 55 in cylinder cap 56. A breather opening 58 in cap 56 provides an exhaust outlet for air in cylinder 40, and it is the function of the valving mechanism to control this exhausting operation as a mean of controlling the feed of abrasive into the main line 12.

' A spring clip 60 mounted on cap 56 presses against stem 54 to lock the plunger 41 in fixed position, and this clip is rotated out of contact with the plunger assembly when the valving mechanism is placed in operation. Since the diameter of plunger 41 is less than that of the cylinder bore, air under pressure admitted to the cylinder by'valve 42 passes between theplunger and cylinder wall and escapes through opening 58.

The operation of the cutting apparatus and in particular the manner in which abrasive particles are fed into the jet stream will be better understood by reference to FIGS. 4, 5 and 6. When handle 36 of main valve 11 is rotated to the open position, the pressure builds up in conduit 12 and hose '14, and air is expelled through opening in nozzle 15. Simultaneously, arm 35 allows relief valve 27 to close and the tank becomes pressurized in the manner of an accumulator. At this point in the operating cycle there is no feeding of the abrasive into conduits 22 or 12.

When the pressure in conduits 12 first builds up, valve head 48 moves up against seat 45a to close the valve, and stem 47 projects up into cylinder 40. The system is then ready for the start of the abrasive feeding operation as shown in FIG. 4.

Spring 60 is now moved out of locking engagement with plunger stem 54 and plunger 41 falls by gravity to the bottom of cylinder 40 where it strikes flange 49 on valve stem 47, unseating valve head 48 and opening the valve, see FIG. 5. As air rushes up through valve insert 45, around plunger 41 and out cap opening 58, there is a momentary sudden drop in pressure in line 12 which exists as long as valve 42 is open. The uprush of air through valve insert 45 upon opening of the valve immediately begins to arrest downward movement of the plunger, and within a very short time interval the pressure against the bottom of the plunger forces the latter upward in the cylinder out of contact with stem 47 so that the valve closes, see FIG. 6. Upon closing of the valve, the pressure in line 12 immediately rises to its original value and remains there until plunger 41 once again falls and opens the valve. A negative pulse of pressure is therefore generated in the system pressure line 12'and this produces a pulse of differential pres.- sure between points A and B in the system.

As the force against the bottom of upwardly moving plunger 41 diminishes with the closing of the valve, the. pull of gravity overcomes the inertia of the plunger and the latter again moves down to begin another cycle.

As soon as valve 42 opens, a differential pressure is applied to abrasive material in tank 19, since the pressure in the tank then exceeds the pressure in conduits 22 and 12. This causes particles of the abrasive to blow through feed opening 24 of extension 23, and into conduit 12. As long as this difference in pressure between points A and -B exists, abrasive material is thus blown into the line, and this feeding action stops when the pressure difference is reduced substantially to zero. The net effect is that a charge of abrasive material measured by the duration of each negative pulse in the pressure line is introduced into the air stream in conduit 12 and is carried to the nozzle as shown in FIG. 6.

The quantity of abrasive material injected into the stream may be controlled by varying the width of the negative pulse of pressure, which is accomplished by adjusting the cycling period of reciprocating plunger 41 as by changing the length of its stroke. This can be accomplished by changing the effective length of cylinder 40 or by varying the weight of the plunger itself. Also, the rate of feed of abrasive into the line may be con trolled by adjusting the amount of the differential pressure as by varying the effective size of exhaust opening 58 in cylinder cap 56.

When the apparatus is shut down, the cam arm 35 opens relief valve 27 as handle 36 of valve 11 is rotated to the off position. This rapidly depressurizes the tank to the atmosphere, thus preventing pressure otherwise captive in the tank from forcing an excessive amount of abrasive through hole 24 and clogging conduits 12 and 22.

It is noted that the only moving parts in the entire system, other than the on-off valves 11 and 27, are plunger 41 and the movable parts of valve 42; and since these moving parts are located ahead of the feed point A in the pressure system, there is little chance that abrasive material can reach and cause excessive wear of these parts. The pulse-type feeding technique of our invention is a positive force-feed system which permits reduction in the diameter of nozzle opening 17 to a minimum. For example, a nozzle open with a diameter of 0.005 inch is feasible with this type of feeding system. This enables correspondingly small widths of cuts with the nozzle. By use of an appropriate length of air line between feed point A and the nozzle opening 17, the intermittently injected charges of abrasive particles become mixed in the line with the result that the discharge from the nozzle is substantially continuous. Suitable orifices, not shown, are located at valve 11 and at nozzle 15 to facilitate control of the air stream and the mixing of the abrasive in it.

Changes, modifications and improvements to the above described preferred embodiment of our invention may occur to those skilled in the art without departing from the spirit of the invention. The appended claims define the scope of the invention.

We claim:

1. Mechanism for mixing a flowable substance with a pressurized gascomprising a conduit, a source of said pressurized gas connected to said conduit, a tank containing said substance connected to said conduit whereby the pressure in the tank is substantially equal to the pressure in the conduit, an exhaust outlet connected to said conduit, valve means for opening and closing said outlet for respectively decreasing and increasing pressure in said conduit, and pressure responsive means operatively connected to said conduit and cyclically operated by the pressure therein, said pressure responsive means having an actuating connection with said valve means whereby the latter cyclically opens and closes said outlet for creating pressure differential pulses in the conduit.

2. Apparatus for feeding a flowable substance into a gas stream comprising a conduit, a source of pressurized gas connected to said conduit, a tank containing said substance connected to said conduit whereby the pressure in the tank is substantially equal to the pressure in the conduit, and a pressure control mechanism connected to said conduit, said mechanism in one operating state connecting said conduit to exhaust and thereby reducing pressure in the conduit below source pressure and in another operating state disconnecting said conduit from exhaust and thereby causing pressure in the conduit to substantially equal the source pressure, said mechanism being responsive to gas pressure for cyclically changing bewteen said operating states for periodically reducing the pressure in said conduit whereby the difference between the pressure in said tank and the pressure in the conduit blows said substance from the tank into the conduit.

3. Pneumatic abrasiVe cutting apparatus, having a source of pressurized air and nozzle for directing a stream of air-abrasive powder mixture against an object to be cut, a main conduit connecting said source to said nozzle, a tank containing the abrasive powder, a feed conduit connecting the interior of the tank to said main conduit so that pressure in the tank is substantially equal to the pressure in the main conduit, and means for periodically reducing the pressure in said main conduit comprising a tubular member connected at one end to said conduit and having an exhaust opening therein, valve means in said member controlling the flow of air from the main conduit to said exhaust opening, a plunger in said member and reciprocable vertically therewithin, said plunger engaging and opening said valve means at one limit of plunger travel and thereby momentarily decreasing the pressure in the main conduit.

4. A valving mechanism comprising an elongated vertically extending hollow cylinder having an exhaust opening at one end and being connected at the other end to a source of air pressure, a valve mounted in said other end of the cylinder controlling the flow of air from said source into said cylinder and having a movable member responsive to source pressure to move to a closed position and block said flow, a plunger disposed in said cylinder and movable vertically therewithin, said plunger being loosely fitted in said cylinder whereby air flowing into said cylinder from said source simultaneously exerts an upward force on said plunger and escapes between the plunger and cylinder to said exhaust opening, said plunger falling in response to gravity and engaging said movable valve member at one limit of plunger travel for opening the valve and disengaging said movable member during upward movement in response to the force of uprushing arr.

5. Abrasive cutting apparatus comprising a main conduit, a source of air pressure connected to one end of said conduit, a nozzle communicating with the other end of said conduit, said nozzle having a small opening through which air passes at high velocity, a main valve in said conduit for pneumatically connecting said source to and disconnecting said source from said conduit, a tank supported above said conduit, an abrasive powder in said tank, a feed conduit connected to said rnain conduit and extending into the bottom of said tank, a feed opening in said conduit through which said abrasive powder passes from said tank to said main conduit, a depressurizing valve connected to the top of said tank, means responsive to the opening and closing of said main valve for respectively closing and opening said depres-surizing valve, and means for periodically reducing the pressure in said main conduit comprising a tubular member connected at one end to said conduit and having an exhaust opening therein, valve means in said member controlling flow of air from the main conduit to said exhaust opening, and a reciprocable plunger in said member for periodically opening said valve means whereby the difference between the pressure in said tank and the pressure in the main conduit blows said powder from the tank through the feed conduit into the main conduit.

6. Pneumatic abrasive cutting apparatus, having a source of pressurized air and nozzle for directing a stream of air-abrasive powder mixture against an object to be cut, a main conduit connecting said source to said nozzle, a tank containing the abrasive powder, a feed conduit connecting the interior of the tank to said main conduit so that pressure in the tank is substantially equal to the pressure in the main conduit, and means for periodically reducing the pressure in said main conduit comprising an exhaust outlet connected to said conduit, valve means controlling said outlet, and a pressure responsive actuator operated solely by the pressure in said conduit for periodically actuating said valve means.

7. Abrasive cutting apparatus comprising a main conduit, a source of air pressure connected to one end of said conduit, a nozzle communicating with the other end of said conduit, said nozzle having a small opening through which air passes at high velocity, a main valve in said conduit for pneumatically connecting said source to and disconnecting said source from said conduit, a tank supported above said conduit, an abrasive powder in said tank, a feed conduit connected to said main conduit and extending into the bottom of said tank, a feed opening in said conduit through which said abrasive powder passes from said tank to said main conduit, and a valving mechanism comprising an elongated vertically extending hollow cylinder mounted above the main conduit, said cylinder having an exhaust opening at the upper end and being connected at the lower end to said main conduit between the main valve and said feed conduit, a valve mounted in the lower end of said cylinder controlling the flow of air from said conduit into said cylinder and having a movable member responsive to pressure in the main conduit for moving to a closed position and blocking said flow, and a vertically reciprocable plunger loosely disposed in said cylinder adapted to engage and open said valve member at one limit of plunger travel.

8. Abrasive cutting apparatus comprising a main conduit, a source of air pressure connected to one end of said conduit, a nozzle communicating with the other end of said conduit, said nozzle having a small opening through which air passes at high velocity, a main valve in said conduit for pneumatically connecting said source to and disconnecting said source from said conduit, a tank supported above said conduit, an abrasive powder in said tank, a feed conduit connected to said main conduit and extending into the bottom of said tank, a feed opening in said conduit through which said abrasive powder passes from said tank to said main conduit, a depressurizing valve connected to the top of said tank, means responsive to the opening and closing of said Inain valve for respectively closing and opening said depressurizing valve; and a valving mechanism comprising an elongated vertically extending hollow cylinder mounted above the main conduit, said cylinder having an exhaust opening at the upper end and being connected at the lower end to said main conduit between the main valve and said feed conduit, a valve mounted in the lower end of said cylinder controlling the flow of air from said conduit into said cylinder and having a movable member responsive to pressure in the main conduit to move to a closed position and block said flow, a plunger disposed in said cylinder and movable vertically therewithin, said plunger being loosely fitted in said cylinder whereby air flowing into said cylinder from said conduit simultaneously exerts an upward force on said plunger and escapes between the plunger and cylinder to said exhaust opening, said plunger falling in response to gravity and being engageable with said movable valve member at one limit of plunger travel for opening the valve and being disengaged from said movable member during upward move ment in response to the force of uprushing air whereby a sudden momentary decrease in pressure occurs in the main conduit.

9. Mechanism for mixing a first flowable substance with a second flowable substance comprising a conduit, a pressurized supply of said second substance connected to said conduit whereby said second substance flows through said conduit under pressure, a closed reservoir containing said first substance connected to said conduit,

the pressure within said reservoir being substantially equal means whereby the latter successively opens and .closes to the pressure in said conduit, an exhaust outlet (3011- said outlet for creating pressure differential pulses in the nected to said conduit, valve means for opening and closconduit. ing said outlet for respectively decreasing and increasing References Cited in the of this patent pressure m said conduit, and pressure responsive means 5 operatively connected to said conduit and cyclically op- UNITED STATES PATENTS er-ated by the pressure therein, said pressure responsive 2,399,680 Keefer May 7, 1946 means having an actuating connection with said valve 2,985,050 Schwacha May 23, 1961 

